Fuels and process for burning them



3,038,299 FUELS AND PROCESS FOR BURNING THEM Charles J. Pedersen, Salem, N.J., assignor to E. 1. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware No Drawing. Filed Dec. 15, 1953, Ser. No. 398,425 17 Claims. (Ci. 6035.4)

This invention relates to fuel compositions and to processes for burning them, and particularly to fuel compositions which are hypergolic with fuming nitric acid and to initiating the ignition of fuels in rockets and like devices.

In the operation of rockets, rocket motors and other devices containing motors operating in like manner, a liquid fuel is injected into a combustion-chamber where it is ignited and burned to form large amounts of gases at high pressure which escape through an exhaust nozzle at high velocity. Usually, the liquid fuel comprises two components-a bulk fuel and an oxidizerwhich are injected into the combustion chamber separately and simultaneously. The bulk fuel usually is a normally liquid hydrocarbon such as gasoline, kerosene, benzene and the like. The oxidizer usually will be a well-known oxidizing agent such as hydrogen peroxide, nitrogen tetroxide and nitric acid. For many applications, white fuming nitric acid has been found to be the most satisfactory. In the operation of such devices, particularly in the operation of rockets, it is essential that the combustion occur immediately and smoothly as the bulk fuel and the oxidizer are injected into the combustion chamber. An electrical ignition system, such as a spark plug or a hot spot, has been used to cause the combustion to start. However, difficulties are often encountered with such electrical systems. Such an electrical system may fail completely or give such a Weak spark as to fail to ignite the fuel when such fuel is of the type most commonly employed heretofore. Such a system may miss, whereupon the-fuel will build up in the combustion chamber so that, when ignition does occur, there is a destructive explosion rather than a smooth combustion. Also, in many cases, it is desirable toeliminate the electrical ignition system so as to reduce the size and Weight of the rocket or like device or to increase its fuel capacity.

It has been proposed to initiate the combustion in the combustion chamber by first introducing a compound which is hypergolic with the oxidizer, i.e. ignites spontaneously upon contact with the oxidizer, and then introducing the bulk fuel into the hot combustion chamber. See Patent No. 2,637,161 to Tschinkel. Such a system has the disadvantage that, when the initiator is used up, ignition within the combustion chamber is no longer assured.

It is an object of this invention to provide new and improved fuel compositions which are hypergolic with fuming nitric acid. A further object is to provide novel methods for burning normally liquid hydrocarbon fuels which are particularly valuable for use in the operation of rockets, rocket motors and like devices. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accomplished in accordance with this invention which comprises mixing a normally liquid hydrocarbon fuel with fuming nitric acid in a combustion zone in the presence of an organic compound which contains the dicyclopentadienyliron nucleus and burning the mixture, and the provision of fuel compositions which are hypergolic with fuming nitric acid and which consist essentially of a normally liquid hydrocarbon fuel and an organic compound which contains the dicyclopentadienyliron nucleus.

nitcd States PatentO I 3,838,299 Patented June 12, 1952 rest hydrogen atoms, amino groups, monoamino alkylradicals of 1 to 12 carbon atoms, and a second dicyclo-' pentadienyliron nucleus joined to the first mentioned dicyclopentadienyliron nucleus by two divalent hydrocarbon bridging radicals each of which contains 1 to 12 carbons, there being no more than 2 such substituents on any one cyclopentadienyl ring.

The substituted dicyclopentadienylirons, which may be employed in accordance with this invention are members of the classes consisting of:

(1) Those in which the substituents consist of 1 to 4 hydrocarbon radicals of 1 to 12 carbon atoms such as bis(methylcyclopentadienyl)iron, (ethylcyclopentadienyl) cyclopentadienyliron, bis(pentylcyclopentadienyl) iron, bis(diphenylcyclopentadienyl)iron and bis(dicyclohexylcyclopentadienyl)iron which may be prepared by the methods disclosed by Graham and Whitman in their copending application Serial No. 352,294, filed April 30, 195 3; (cyclopentenylcyclopentadienyl) (cyclopentadienyl) iron, a yellow crystalline solid melting at '6667 C. and (cyclopentylcyclopentadienyl) (cyclopentadienyl)iron, a yellow oil freezing at l5-16 C., boiling at 165 C. at 10 mm., giving a yellow color in sulfuric acid turning to green which are prepared by the methods disclosed by Weinmayr in his copending application Serial No. 388,703, filed October 27, 1953, now vPatent No.

2,831,879, Patented April 22, 1958; (cyclopentadienyl) (phenylcyclopentadienyl)iron, bis(phenylcyclopentadienyl)iron, tri(p-diphenyl)bis(cyclopentadienyl)iron and bis(p-diphenylcyclopentadienyl)iron which may be prepared by the methods disclosed by Weinm'ayr in his copending application Serial No. 352,283, filed April 30, 1953 (now abandoned);

(2) Those in which the substituents consist of a second dicyclopentadienyliron nucleus joined to thefirst such nucleus by two divalent hydrocarbon bridging radicals each of which contains 1 to 12 carbon atoms, such as methylene and phenylmethylene bridging radicals, which is the condensation product of two moles of dicyclopentadienyliron with two moles of an aldehyde, e.g. formaldehyde, with the elimination of two moles of water and which may be prepared by the methods disclosed by Weinmayr inhis copending application Serial No. 312,851, filed October 2, 1952, now Patent No. 2,- 694,721, patented November 16, 1954;-

(3) Those in which the substituents consist of mono-. halogenated hydrocarbon radicals of 1 to 12 carbon atoms in which the halogen atom has an atomic weight of at least 35 (chlorine, bromine and iodine), preferably chlorine, such as (p chlorophenylcyclopentadienyl) (cyclopentadienyDiron and his (p chlorophenylcyclopentadienyl)iron which may be prepared by the methods disclosed by Weinmayr in. his copending application Serial No. 352,283, filed April 30, 1953 (now abandoned);

(4) Those in which the substituents are organic radicals consisting of 1 to 12 carbon atoms, 1 oxygen atom and the rest hydrogen atoms, such as the carboxaldehydes, represented by cyclopentadienyl('aldomethylcyclopentadienyl) iron and bis(aldomethylcyclopentadienyl)iron which may be prepared by the methods disclosed by Graham in his copending application Serial No. 360,370, filed June 8, 3, now Patent No. 2,849,469, patented August 26, 1958;

the acyl derivatives, represented by (acetylcyclopentadi' 7 4 5 Those in which enyl) (cyclopentadienyl)iron which may be prepared by themethod disclosed by Weinmayr in his copending application Serial No. 352,029, filed April 29, 1953, new

- Patent No. 2,988,562 patented June 13, 1961 and by b.is(acetylcyclopentadienyl)iron which may be prepared by the method disclosed by Woodward et al. in J .A.C.S. 74, 3458 (1952); the hydroxy alkyl derivatives, represented by cyclopentadienyl(hydroxymethyl cyclopentadienyl) iron and cyclopentadienyl(alphadaydroxyethyl cyclopentadienyl)iron which may 'be made by the methods disclosed by Alfred C. Haven, Jr. in his copending ap- Serial No. 365,558, filed July 1, 1953, now

plication I 7 Patent No. 2,810,737, Patented October 22,1957; the

, hydroxyaryl derivatives, represented by (cyclopentadienyl) .alkylradicals of l to 12 carbon atoms, represented by (aminoethyl cyclopentadienyl)cyclopentadienyliron,which.

may be prepared by the methods disclosed by Graham and Whitman in their 'copending application Serial No. 365,563, filed July 1, 1953, no-W Patent No. 2,859,233, patented November 4, 1958; a b

(7) Those in which there are 2 to 4 different substituents selected from inclusive, above; and b (8) Mixtures of 2 or more of dicyclopentadienyliron and such substituted dicyclopentadienylirons.

It has been found that such organic compounds, containing the dicyclopentadienyliron nucleus, are hypergolic with fuming nitric acid. Thatis, when such compounds are brought into contact with fuming nitric acid, spontaneous ignition occurs immediately and combustion continues with great vigor. When fuming nitric acid is added to a normally liquid hydrocarbon fuel under standard conditions, the nitric acid oxidizes the hydrocarbon with the evolution of fumes of oxides of nitrogen but usually without spontaneous combustion. If the fuel contains as littel as 0.1% by weight of dicyclopentadienyliron compound of this invention in the solid, i.e. undissolved state, dispersed in or covered by the fuel, the addition of a small proportion of fuming nitric acid thereto results in vigorous spontaneous combustion of the mixture; i.e. normally liquid hydrocarbon fuels containing at least 0.1% by Weight of such dicyclopentadienyliron compounds in the solid state are hypergolic with fuming nitric acid. Similar dispersions of solid dicyclopentadienyliron compounds in other readily combustible organic liquids are likewise hypergolic with fuming nitric acid. By a readily combustible organic liquid or solvent, is meant one which has such characteristics of combustibility as would obviously render it suitable for use as a, fuel or as a component of a fuel.

Solutions of such dicyclopentadienyliron compounds in readily combustible organic solvents, in which the dicyclopentadienyliron compound is in a concentration of at least 25% by weight,-are also hypergolic with frmiing nitric acid.

compound is completely dissolved in anormally liquid hydrocarbon fuel in a concentration materially less than 25% by Weight, the composition is not hypergolic with fuming nitric acid. However, when the fuel contains the dicyclopentadienyliron compound in solution in a concentration of about 5% or more by Weight but insufficient to render the fuel hypergolic with fuming nitric acid, the addition of fuming nitric acid thereto produces much more vigorous fuming of the mixture than is obtained in Jr., in'his copending applica fuming increasing with increase in theconcentration of compounds in the solid state, (2)

drocarbon fuels containing at least by weight of one theclass as set forth in- (l) to (6) I iron compound;

the absenceof the dicyclopentadienyliron compound, the

the dicyclopentadienyliron compound in the fuel. This indicates that the dicyclopentadienyliron compoundmaterially increases the rate of oxidation by the nitric acid whereby the fuel appears to be greatly activated and, it is firmly believed,.the mixture will be ignited by very weak'sparksin sufficientlystrong to causeignition in the absence of the dicyclopentadienyliron compound.

The readily combustible organic liquids and solvents I include, in addition to the normally liquid hydrocarbon fuels aromatic and aliphatic hydrocarbons generally, alcohols, ethers, petroleum ether, ketones, and esters.

The novel fuel compositions, which are hypergolic with. fuming nitric acid and which constitute an important feature of this invention, consist essentially of (1) normally liquid hydrocarbon fuels containing at least 0.1%

or more of the dicyclopentadienyliron,

by weight of one normally liquid hyor. more of the dicyclopentadienyliron compounds in the form of a solution, and (3) mixtures of (1) and (2').

' When the dicyclopentadienyliron compound is in the solid state, the fuel composition (1) may, and usually will, contain some of the compound in solution. When the dicyclopentadienyliron compound is in the form of a solution (2), it may be dissolved in the hydrocarbon fuel alone or, in whileor in part, in another readily combustible organic solvent therefor which is miscible with the hydrocarbon fuel, it being understood that the percent by weight of the dicyclopentadienyliron compound is based on the total of hydrocarbon fuel, other readily combustible organic solvent (when present), and dicyclopentadienyl- Dicyclopentadienyliron is soluble in high concentrations in the normally liquid hydrocarbon fuels and in 7 common organic solvents such as aromatic and aliphatic hydrocarbons, alcohol, ether and the like. The substh tuted dicyclopentadienylironsare of varying solubilityin the fuels and some require additional solvents when it is desired to incorporate them in the fuels in high concentrations as solutions. The literature and application disclosures of the compounds and of the methods of making them, hereinbefore referred to, also disclose suitable solvents therefor, including aliphatic and aromatic hydrocarbons such as petroleum ether, gasoline, benzene and Xylene, alcohols such as methyl alcohol, ethyl alcohol and butyl alcohol, ethers suchas methyl ether and ethyl ether, and the like.

Broadly, the process of this invention comprises mixing a normally liquid hydrocarbon fuel with fuming nitric acid in a combustion zone in the presence of one or more of the dicyclopentadienyliron compounds and burning the i On the other hand, when the dlcyclopentadienyliron" mixture. The means and modes for carrying out such process may be widely varied.

When the fuel composition is hypergolic with fuming nitric acid, the fuel composition and the fuming nitric acid may be fed directly, but separately, and simultaneously into the combustion chamber employing an apparatus such as that disclosed by Tschinkel in Patent No. 2,637,161, whereupon the fuel composition and the fuming nitric acid will mix and spontaneously ignite and burn vigorously to form the large volume of gases required for propelling the rocket or like device. When the fuel composition is not hypergolic with fuming nitric acid, that is, whenit contains 5% or more of a dicyclopentadienyliron compound but insufficient to render the fuel composition pentadienyliron compound in powderedform ora dispersion or solution of the dicyclopentadienyliron compound in a readily combustible organic liquid in such form and concentration as to render the dispersion or solution hypergolic with fuming nitric acid. In such case, the bulk fuel may be devoid of dicyclopentadienyliron compound or contain dicyclopentadienyliron compound in an amount insufficient to render the fuel composition hypergolic with the fuming nitric acid. Under these circumstances, the powdered dicyclopentadienyliron compound or the hypergolic dispersion or solution thereof will first contact the fuming nitric acid, ignite and burn vigorously and the bulk fuel will be fed into such burning mixture whereby the bulk fuel will also be ignited and caused to burn. Still other means or types of apparatus and procedures for carrying out the process of this invention will be apparent to those skilled in the art.

In order to more clearly illustrate this invention and the advantageous results to be obtained thereby, the following examples are given in which the fuel is a refined kerosene which has had the aromatic and naphthenic hydrocarbons removed in order to reduce smoking tendencies and is known as J P-4 rocket fuel and which is completely described in Petroleum Processing Magazine, October -1 95 2, page 1426.

Example 1 A small amount (about 20 cc.) of a kerosene based fuel characterized as J P-4-was placed in a shallow porcelain dish. About 0.1 g. of crystalline dicyclopentadienyliron was added to the dish containing the fuel and the solid crystals allowed to settle to the bottom. Another porcelain dish containing the same rocket fuel, but without the dicyclopentadienyliron, was used as a control. Fuming nitricacid about 1 cc.) was added to each of the two dishes. The fuel, in the dish containing the dicyclopentadienyliron in solid crystalline form, immediately burst into flames and continued to burn fiercely. The control fiuel, Without dicyclopentadienyliron, did not ignite.

It is thus evident that the presence of solid particles of vdicyclopentadienyliron will enhance the activity of a rocket fuel. As already indicated, the solid compound may be dispersed in the fuel or sprayed into the rocket combustion chamber.

When the experiment was repeated with a 5% solution of dicyclopentadienyliron in the fuel and fuming nitric acid as before, the fuel did not ignite, but fumed much more vigorously than the control. It is thus evident that the fuel was considerably activated by the low concen tration of dissolved dicyolopentadienyliron.

Example 2 When cyclopentadienyl(ethylcyclopentadienyl)iron, alone and as solutions in the fuel, was treated with fuming nitric acid as described in Example 1, the following results were obtained:

I ln each of (c), (d) and (2), the iron compound was completely dissolved in the fuel.

. Example 3 The experiments of Example 2 were repeated, with solutions of cyclopentadienyl(cyclopentylcyclopentadienyl)iron in the fuel, with the following results:

White fuming nitric Cyelopentadienyl(cycl0- pentylcyclopentadienyl)- iron (parts by Weight) Weight percent of iron acid deriva- (parts by tive in weight) fuel Kerosene based fuel (parts by weight) Result Did not fire. 16. 7 Fired immediately. do 1 do 50 Orb-1 [Obmen mm Example 4 The experiment of Example 1 in which the iron compound Was dispersed in the fuel, was repeated with acetylcyclopentadienyl:(cyclopentadienyl)iron. The results obtained follows:

(a) When fuming nitric acid was added to solid acetylcyclopentadienyl(cyclopentadienyl)iron, the mass burst into flames.

b) When fuming nitric acid was added to a slurry of 0.5% by Weight of acetylcyclopentadienyl(cyclopentadienyl)iron in J P-4, the mixture burst into flames and burned violently.

(c) When fuming nitric acid was added to a 10% solution of the iron compound in J P-4, no ignition occurred, but much more vigorous fuming occurred in comparison to a control containing no iron compound.

Example 6 Dicyclopentadienyliron was melted in a test tube and allowed to 0001 until solid. A small lump of the solid, weighing 20 mg, was placed at the bottom of a porcelain dish and 20 g. of J P-4 added. This represents a 0.1% concentration of the iron compound. When about 3 g. of nitric acid is added to the fuel near the solid, the fuel bursts into flame and burns vigorously until consumed.

Example 7 The following compounds are used to activate JP-4 fuel in the manner previously described: (aminocyclopentadienyl)(cyclopentadienyl)iron, (cyclopentadienyl)(phydroxyphenylcyclopentadienyl)iron, bis(phenylcyclopentadienyl)iron, =bis(p-chlorophenylcyclopentadienyl)- iron, and the product of the reaction between dicyclopentadienyliron and formaldehyde.

About 10 to 20 mg. of the solid iron derivative is covered with 3 g. of JP-4 and 0.5 to 1.0 g. of fuming nitric acid is added. In all cases, ignition occurs immediately.

It will be understood that the preceding examples have been given for illustrative purposes solely and that many variations and modifications can be made in the compositions, the proportions thereof and the modes and apparatus employed for bringing the fuel, the dicyclopentadienyliron compound and the fuming nitric acid together in a combustion chamber under conditions such that ignition and combustion will occur, Within the scope of the general description without departing from the scope or spirit of this invention.

From the preceding disclosure, it will be apparent that,

by this invention, there has been provided novel fuel compelled or otherwise motivated by expelling, through an exhaust nozzle at high velocity, large volumes of gases formed by the combustion of a liquid fuel in a combustion chamber. Also, this invention provides a novel and valuable process for burning normally liquid hydrocarbon fuels at least in part by the action of nitric acid thereon in the presence of a novel class of hypergolic compounds which initiate and/ or greatly promote and maintain the combustion. Accordingly, it is apparent that this invention constitutes a valuable contribution to and advance in the art.

What is claimed is:

1. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form at least 0.1% by weight of an organic compound containing the dicyclopentadienyliron nucleus which is a member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of l to 4 members of the group consisting of an alkyl radical of l to 12 carbon atoms, the chlorophenyl radical, the aldomethyl radithe cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenll radical, the aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6-l2 carbon atoms, the amino group, and a monoaminoalkyl radical of 1 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

2. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by weight of an organic compound containing the dicyclopentadienyliron nucleus which is a member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 members of the group consisting of an alkyl radical of 1 to 12 carbon atoms, a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenyl radical, the aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6-12 carbon atoms, the amino group, and a monoaminoalkyl radical of 1 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

3. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by weight of dicyclopentadienyliron.

4. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by weight of a substituted dicyclopentadienyliron in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 aryl radicals of 6 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

5. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by weight of bis(phenylcyclopentadienyDiron.

6. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by Weight of a substituted dicyclo- 8 M pentadienyliron in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 lower alkyl acyl radicals, there being no more than two of such substituents on any one cyclopentadienyl ring.

7. A fuel composition hypergolic with fuming nitric acid which consists essentially of a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by weight of a'cetylcyclopentadienyl- (cycloperitadienylfiron.

8. A process for burning a normally liquid hydrocarbon fuel which comprises bringing together and burning in the presence of the fuel fuming nitric acid and in undissolved form at least 0.1% by Weight based on the fuel of an organic compound containing the dicyclopentadienyl nucleus which is a member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 members of the group consisting of an alkyl radical of 1 to 12 carbon atoms, a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenyl radical, the aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6-12 carbon atoms, the amino group, and a monoaminoalkyl radical of 1 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

9. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to spontaneously ignite and burn, and injecting the bulk fuel into the resulting burning composition, the hypergolic composition being a member of the group consisting of an organic compound containing the dicyclopcntadienyliron nucleus and a dispersion of at least 0.1% by weight of said organic compound in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons, lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers, said organic compound being a member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 members of the group consisting of an alkyl radical of 1 to 12 carbon atoms, a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenyl radical, the aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6 to 12 carbon atoms, the amino group, and a monoaminoalkyl radical of 1 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

10. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to spontaneously ignite and burn, and injecting the bulk fuel into the resulting burning, composition, the hypergolic composition being a member of the group consisting of an organic compound containing the dicyclopentadienyliron nucleus and a dispersion of 0.1% to about 50% by weight of said organic compound in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons, lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers, said organic compound being a 9 member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 members of the group consisting of an alkyl radical of l to 12 carbon atoms, a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenyl radical, the aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6 to 12 carbon atoms, the amino group, and a monoaminoalkyl radical of 1 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

11. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to spontaneously ignite and burn, and injecting the bulk fuel into the resulting burning composition, the hypergolic composition being a member of the group consisting of dicyclopentadienyliron and a dispersion of 0.1% to about 50% by weight of dicyclopentadienyliron in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons, lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers.

12. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to spontaneously ignite and burn, and injecting the bulk fuel into the resulting burning composition, the hypergolic composition being a member of the group consisting of an organic compound containing the dicyclopentadienyliron nucleus and a dis persion of 0.1% to about 50% by weight of said organic compound in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons, lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers, said organic compound being a substituted dicyclopentadienyliron in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 aryl radicals of 6 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

13. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to spontaneously ignite and burn, and injecting the bulk fuel in to the resulting burning composition, the hypergolic composition being a member of the group consisting of bis(phenylcyclopentadieny1)iron and a dispersion of 0.1% to about 50% by weight of bis(phenylcyclopentadienyl)iron in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons, lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers.

14. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to spontaneously ignite and burn, and injecting the bulk fuel into the resulting burning composition, the hypergolic composition being a member of the group consisting of an organic compound containing the dicyclopentadienyliron nucleus and a dispersion of 0.1% to about 50% by weight of said organic compound in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons,

lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers, said organic compound being a substituted dicyclopentdienyliron in which the substituents are on the cyclopentadienyl rings and consist of l to 4 lower alkyl acyl radicals, there being no more than two of such substituents on any one cyclopentadienyl ring.

15. A process for burning a bulk fuel which is a normally liquid hydrocarbon fuel, which comprises bringing together in a combustion zone fuming nitric acid and a composition which is hypergolic with the fuming nitric acid and causing the composition to sponetaneously ignite and burn, and injecting the bulk fuel into the resulting burning composition, the hypergolic composition being a member of the group consisting of acetylcyclopentadienyl (cyclopentadienylfiron and a dispersion of 0.1% to about 50% by weight of acetylcyclopentadienyl(cyclopentadienyl)iron in undissolved form in a readily combustible organic liquid of the group consisting of hydrocarbons, lower saturated aliphatic monohydric alcohols and lower saturated aliphatic ethers.

16. A process for burning a normally liquid hydrocarbon fuel which comprises simultaneously injecting into a combustion zone fuming nitric acid and a normally liquid hydrocarbon fuel having dispersed therein in undissolved form at least 0.1% by weight of an organic compound containing the dicyclopentadienyliron nucleus which is a member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of 1 to 4 members of the group consisting of an alkyl radical of 1 to 12 carbon atoms, a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenyl radical, the aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6 to 12 carbon atoms, the amino group, and a monoaminoalkyl radical of 1 to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

17. A process for burning a normally liquid hydrocarbon fuel which comprises simultaneously injecting into a combustion zone fuming nitric acid and a normally liquid hydrocarbon fuel having dispersed therein in undissolved form 0.1% to about 50% by weight of an organic compound containing the dicyclopentadienyliron nucleus which is 'a member of the class consisting of dicyclopentadienyliron, two dicyclopentadienyliron nuclei joined by two divalent bridging radicals selected from the group consisting of methylene and phenylmethylene radicals, and substituted dicyclopentadienylirons in which the substituents are on the cyclopentadienyl rings and consist of l to 4 members of the group consisting of an alkyl radical of l to 12 carbon atoms, a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenyl radical, the 'aldomethyl radical, a lower alkyl acyl radical, a lower monohydroxy alkyl radical, a monohydroxyaryl radical of the benzene series which contains 6 to 12 carbon atoms, the amino group, and a monoaminoalky-l radical of l to 12 carbon atoms, there being no more than two of such substituents on any one cyclopentadienyl ring.

References Cited in the file of this patent Trent et al.: Journal of the American Rocket Society, vol. 21, Sept. 1951, pp. 129-131. (Copy in Scientific 7 Library.)

Nature, Dec. 15, 1951, pages 1039, 1040. Miller et 'al.: Journal of Chemical Society (London), Feb. 1952, pp. 632-635.

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 3,038,299 June 12, 1962 Charles J. Pedersen It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 54, after "solid" insert i.e. undissolved column 4, line 8, for "in sufficiently" read insufficiently line 28, for "while" read whole column 7, line 25, after 'atoms," insert a cycloalkyl radical of 5 to 6 carbon atoms, the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, column 7, lines 26 and 27, strike out "the cyclopentenyl radical, an aryl radical of 6 to 12 carbon atoms, the chlorophenll radical, the aldomethyl radi- Signed and sealed this 2nd day of October 1962.

SEAL) ttest:

ERNEST W. SWIDER DAVID L. LADD Attcsting Officer Commissioner of Patents 

8. A PROCESS FOR BURNING A NORMALLY LIQUID HYDROCARBON FUEL WHICH COMPRISES BRINGING TOGETHER AND BURNING IN THE PRESENCE OF THE FUEL FUMING NITRIC ACID AND IN UNDISSOLVED FROM AT LEAST 0.1% BY WEIGHT BASED ON THE FUEL OF A ORGANIC COMPOUND CONTAINING THE DICYCLOPENTADIENYL NUCLEUS WHICH IS A MEMBER OF THE CLASS CONSISTING OF DICYCLOPENTADIENYLIRON, TWO DICYCLORENTADIENYLIRON NUCLEI JOINED BY TWO DIVALENT BRIDGING RADICALS SELECTED FROM THE GROUP CONSISTING OF METHYLENE AND PHENYLMETHYLENE RADICALS, AND SUBSTITUTED DICYCLOPENTADIENYLIRONS IN WHICH THE SUBSTITUENTS ARE ON THE CYCLOPENTADIENYL RINGS AND CONSIST OF 1 TO 4 MEMBERS OF THE GROUP CONSISTING OF AN ALKYL RADICAL OF 1 TO 12 CARBON ATOMS, A CYCLOALKYL RADICAL OF 5 TO 6 CARBON ATOMS, THE CYCLOPENTENYL RADICAL, AN ARYL RADICAL OF 6 TO 12 CARBON ATOMS, THE CHLOROPHENYL RADICAL, THE ALDOMETHYL RADICAL, A LOWER ALKYL ACYL RADICAL, A LOWER MONOHYDROXY ALKYL RADICAL, A MONOHYDROXARYL RADICAL OF THE BENZENE SERIES WHICH CONTAINS 6-12 CARBON ATOMS, THE AMIMO GROUP, AND A MONOAMINOALKY RADICAL OF 1 TO 12 CARBON ATOMS, THERE BEING NO MORE THAN TWO OF SUCH SUBSTITUENTS ON ANY ONE CYCLOPENTADIENYL RING. 